BEIJING—China’s government has substantially increased spending on domestic security, official figures show, reflecting mounting concern about threats inside its borders as President Xi Jinping moves to acquire more power and reassert the authority of the Communist Party.

Beijing’s budgets for internal and external security have grown faster than the economy as a whole for several years, but domestic security spending has grown far faster—to where it exceeds the national defense budget by roughly 20%.

Across China, domestic security accounted for 6.1% of government spending in 2017, the Ministry of Finance said. That translates into 1.24 trillion yuan ($190 billion) and compares with 1.02 trillion yuan in central government funding for the military.

The numbers, revealed in an annual budget report released this week, help illustrate the scale of a recent ramping up of security and surveillance across China, particularly in Xinjiang and Tibet, minority-heavy areas on the country’s periphery.

In Xinjiang the government has woven a web of surveillance, with checkpoints, high-definition cameras, facial scanners and street patrols; the region spent $9.1 billion on domestic security in 2017, a 92% increase from 2016, according to local government budget data.

Spending across the country on domestic security rose 12.4% last year; in 2016, spending increased 17.6%, official data show.

The budget for domestic security covers regular and paramilitary police, courts, prosecutors and prisons. Chinese authorities are experimenting with cutting-edge tracking tools, tapping into social-media accounts to punish politically incorrect speech and, in some places, trying to get residents to inform on each other using smartphone apps.

The spending numbers are “very consistent with the heavy securitization that’s going on,” said Adrian Zenz, a lecturer at the European School of Culture and Theology in Germany who studies China’s security apparatus.

The Finance Ministry stopped including the domestic-security budget in its annual report in 2013, after media reports highlighted its growth. This year, the number appeared only as a percentage of the total budget in a graph and wasn’t mentioned in the text. It isn’t clear why the ministry decided to publish the number again.

The budget report was released as China’s National People’s Congress convenes in Beijing, where delegates are set to approve changes to the country’s constitution that would permit Mr. Xi to remain president for as long as he wishes.

Premier Li Keqiang, addressing the legislature on Monday in an annual government work report, highlighted a crime crackdown called the “Peaceful China initiative,” vowing to stamp out terrorism, violent crime, pornography, gambling and other scourges.

“With these steps we will safeguard national and public security,” he said.

The security escalation is particularly striking in Xinjiang, in China’s far west, where the government has armed tens of thousands of police with the latest technology. Cameras and checkpoints blanket the region’s cities and villages, and street patrols use hand-held devices to scan ID cards and smartphones.

Authorities have invested in data platforms used to identify “unsafe” members of the region’s Uighur population, and in construction of a network of detention centers.

Xinjiang’s police are also engaged in a blood-collection effort designed to further expand China’s DNA database, already the world’s largest.

Per capita security spending in Xinjiang and the Tibetan Autonomous Region to the south are comparable to the national average in the U.S., with adjustments for differences in costs for personnel and equipment, said Mr. Zenz. The U.S. spends around $570 per person on policing and other forms of law enforcement, Mr. Zenz says in an article to be published soon by the Jamestown Foundation.

Children and police watch passing Buddhist monks during a ceremony on March 1 in China’s Tibetan Autonomous Region, where authorities have invested in surveillance and policing. Photo: JOHANNES EISELE/AGENCE FRANCE-PRESSE/GETTY IMAGES

Chinese officials say the increase in surveillance Xinjiang and Tibet is necessary to snuff out separatist movements among minority groups they say are influenced by hostile forces abroad. Human-rights groups say discriminatory policies in both regions are partly to blame for ethnic strife and that the heavy security exacerbates the tension.

China’s military is also investing heavily to develop its capabilities and this week unveiled its largest annual increase in spending in three years—an 8.1% rise, after a 7% increase in 2017.

That pales with the ramp-up in policing at home. “Growth in China’s defense budget remains in the single digits, and broadly in line with economic conditions,” said William Choong, an Asian security specialist at the International Institute for Strategic Studies, a security think tank. “A one-percentage-point increase isn’t much to shout about.”

In China, as in many other countries, actual spending on internal and external security is likely higher than official budget numbers suggest, according to Mr. Zenz and other analysts.

Chinese police in the old city of Kashgar, Xinjiang, where surveillance has escalated to monitor the local Uighur population. Photo: GIULIA MARCHI FOR THE WALL STREET JOURNAL

The Ministry of Finance said in its budget report that domestic security spending would decrease slightly as a proportion of total spending this year. That is based on the budget; last year domestic security agencies went 22.9% over budget, according to the National Bureau of Statistics.

Neither the Ministry of Finance nor the Ministry of Public Security responded to requests for comment.

A significant portion of this year’s expenses likely came from payments for infrastructure such as new police stations and big-data platforms, said Mr. Zenz.

His research into the growing security apparatus in Xinjiang and elsewhere has included the compiling of authorities’ advertising of new police positions. In Xinjiang, around 100,000 new positions were announced in a one-year period to September 2017, and the advertising for more police continues, he said.